There are cases where an area of high brightness (brightness area) and an area of low brightness (dark area) are mixedly present within image data imaged by an imaging device such as a camera. For example, when an area having the bright outside due to sunlight and an area having the dark inside are included, a sufficient difference of light and shade between the brightness area and the dark area. However, there is a problem in that contrast is not uniformly set within the areas and an imaging subject is not vivid.
In consideration of such a problem, there is a known technology in which histogram data indicating tone distribution of pixels present within a local area centering around a certain observation point, on an image is generated, a tone conversion curve (a tone curve) enhancing the contrast of the tone of a high degree in the histogram data is obtained, and tone correction processing is performed by applying the tone conversion curve, that is, the tone correction processing performed through a so-called local histogram equalization method. Accordingly, the contrast is enhanced in each area of the brightness area and the dark area, and a vivid image can be obtained.
Incidentally, when the tone correction processing by the local histogram equalization method is performed on the basis of a pixel unit with respect to an entire image, a massive computation amount is required, and thus, the method is not practically suitable for the purpose of an application for image processing in daily use.
There is a known technology in which the tone correction processing is performed by dividing image data into multiple blocks, counting a representative value of each block included in a local area centering around each block, generating histogram data of each block, and obtaining the tone conversion curve based on the histogram data (for example, refer to PTL 1). According to an image processing device disclosed in PTL 1, the computation amount can be reduced.